Aircraft manufacturers continually strive for ways to increase aircraft performance and reduce manufacturing costs. One well-known method for increasing aircraft performance is to reduce airframe weight through the use of state-of-the-art materials, such as composites, having relatively high strength-to-weight ratios. Conventional methods for manufacturing airframes with composite materials, however, often require relatively expensive tooling and labor-intensive assembly procedures.
FIG. 1 is an isometric view of a metal aircraft panel 100 configured in accordance with the prior art. The panel 100 includes a frame 106 and a plurality of stringers 104 attached to a skin 102 in a “semi-monocoque” configuration. The stringers 104 are “hat-section” stringers having a raised portion 103 and opposing flange portions 105. The flange portions 105 are attached directly to the skin 102.
The frame 106 includes a first frame section 107 and a second frame section 108. The first frame section 107 includes a base portion 109 and an upstanding leg portion 110. The upstanding leg portion 110 is fastened to the second frame section 108, and includes a plurality of openings or “mouse holes” 114 through which the raised portions 103 of the stringers 104 extend. The base portion 109 is attached to the stringer flange portions 105 and the skin 102. The base portion 109 includes a plurality of steps or “joggles” 112 positioned just outboard of the stringer flange portions 105. The joggles 112 allow the base portion 109 to step off of the stringer flange portions 105 and onto the skin 102. This allows the base portion 109 to be fastened directly to the skin 102 between the stringers 104 without causing gaps or excessive preload between the base portion 109 and the skin 102.
One shortcoming of the prior art panel 100 is that it can be expensive to manufacture. Forming the joggles 112 in the first frame section 107, for example, adds additional cost when compared to a similar frame section without joggles. This is especially true if the first frame section 107 is manufactured from composite materials rather than metal, because forming joggles in composite materials typically requires special tooling and/or post-cure machining.